Poly-3-hydroxybutyrate polymers are obtained using plants as a raw material, and therefore are recently noted as a material having small environmental load. However, the poly-3-hydroxybutyrate polymers have the problem of having poor impact resistance.
To overcome this problem, a method of mixing polycaprolactone or polybutyrene succinate resin is proposed as described in, for example, JP-A-9-194281 and JP-A-11-323141.
However, in the method of mixing a different kind of polymer as proposed in the above-described patent publications, a composition thus obtained does not have sufficient impact resistance, and further has poor heat resistance.